1. Field of the Invention
The present invention relates in general to a photoresist coating system. In particular, the present invention relates to a bubble detection system to detect photoresist bubbles in the pipes of the photoresist coating system.
2. Description of the Related Art
Because most available photoresists are liquid, it is necessary to pump photoresist from a reservoir to a reactor where photoresist is dispensed and coated on a wafer. Moreover, in most present photoresist coating systems, not only are both pump and pipeline used, but also a tank is situated along the pipeline to adjust flow rate of the photoresist before it enters the pump and is sent to the reactor. In other words, the photoresist coating system is designed to allow continual and uniform application to the wafer.
Of course, owing to the fact that in many contemporary semiconductor processes several kinds of photoresists are required, most available photoresist coating systems comprise several pumps, several reservoirs and several tanks, and only one reactor. However, only one reservoir, one pump, one tank and one pipeline are required for each type of photoresist.
It is well known that formation of the photoresist layer is affected by bubbles in the photoresist. When bubbles enter the pump, they are also sent into the reactor. Thus, the quantity of photoresist dispensed on the wafer is fluctuant and the distribution of photoresist on the wafer is also inconsistent, such that the quality of the photoresist layer is compromised by the bubbles. In addition, the bubbles are caused by incomplete sealing of photoresist coating system pipelines and improper operation of the system pump.
To avoid these disadvantages, conventional photoresist coating systems normally use a sensor to detect the presence of bubbles.
FIG. 1 shows the structure of the conventional bubble detection system. The devices of the conventional bubble detection system are connected by pipes.
There is photoresist stored in the photoresist tank 10. N2 is injected into the photoresist tank 10 through the N2 connector 10A to force the photoresist to the L/E tank 12. There is another input terminal (drain) 12A to provide photoresist to the L/E tank 12. A L/E sensor 14 is set between the photoresist tank 10 and the L/E tank 12 to detect bubbles in the pipes therein. The buffer tank 16 stores the photoresist from the L/E tank 12, the drain 16A drains the air out from the buffer tank 16. The pump 18 presses the photoresist in the pipe to the nozzle 19 through the filter 17 to perform the semiconductor processes. The bubble sensor 15 is set between the buffer tank 16 and the pump 18 to detect bubbles in the pipes. When the L/E sensor 12 and the bubble sensor 15 detect bubbles, an alarm instructs the operator to stop the process.
However, in the conventional bubble detection system, the L/E sensor is set in the front terminal of the bubbles detecting system. Thus, if there are bubbles in the L/E tank or in the buffer tank, the system still works and causes poor coating. Actually, the source of bubbles comprises the incomplete sealing of pipelines of the photoresist coating system and improper operation of the pump of the photoresist coating system. If the bubbles aren""t detected, the coating effect is deteriorated.
The object of the present invention is to provide a bubbles detection system, which comprises an additional bubble sensor between the buffer tank and the pump to detect bubbles in the end terminal of the pipe.
Another object of the present invention is to provide a bubbles detection system, which continues to generate conspicuous alarm signals to warn the user to clean the bubbles from the system when detecting the bubbles.
To achieve the above-mentioned object, the present invention provides a bubble detection system to detect bubbles in photoresist, comprising photoresist tanks, a buffer tank, a pump, a bubble sensor, and a nozzle. The photoresist tank provides the photoresist. The buffer tank stores the photoresist from the photoresist tank. The pump pumps the photoresist from the buffer tank to an end terminal. The bubble sensor is set between the buffer tank and the pump to detect bubbles in the photoresist, and outputs an alarm signal when bubbles are detected. The nozzle is set at the end terminal to output the photoresist.
Moreover, the present invention provides a bubble detection system for detecting bubbles in a photoresist pipe, comprises a relay, a first indicating device, a sensor a second indicating device, and a third indicating device. The relay comprises a magnetic switch and a magnetic string. The magnetic switch comprises a first terminal coupled to a first power source and a second terminal, and the magnetic string is coupled between the second terminal and ground. The first indicating device is coupled to the second terminal to output a first alarm signal according to a signal. The sensor is coupled between the first terminal and the second terminal to sense the pipe and outputs the sensing signal to the first indicating device and the magnetic string to turn on the magnetic switch when bubbles are detected. The second indicating device outputs a second alarm signal when the magnetic switch is turned on. The third indicating device is coupled to a second power source to output a third alarm signal when the magnetic switch is turned on.